Assessing the physical reality of Milky Way open cluster candidates

Abstract

We report results on the analysis of 11 new Milky Way open cluster candidates, recently discovered from the detection of stellar overdensities in the Vector Point diagram, by employing Xtreme deconvolution Gaussian mixture models. We treated these objects as real open clusters and derived their fundamental properties with their associated intrinsic dispersions by exploring the parameter space through the minimization of likelihood functions on the generated synthetic colour-magnitude diagrams. The intrinsic dispersions of the resulting ages turned out to be much larger than those usually obtained for open clusters. Indeed, they resemble the ages and metallicities of composite star field populations. We also traced their stellar number density profiles and mass functions and derived their total masses and Jacobi and tidal radii, which helped us as criteria while assessing their physical nature as real open clusters. Because the 11 candidates show a clear gathering of stars in the proper-motion plane and some hint for similar distances, we concluded that they are possibly sparse groups of stars.